JPH06100319A - Multiple oxide with perovskite structure and its production - Google Patents

Abstract

PURPOSE:To provide the subject multiple oxide high in catalytic activity and adsorptive activity etc. CONSTITUTION:The objective multiple oxide with perovskite structure of formula M<1>M<2>1-XM<3>O3 (M<1> is La, Sr, Ce, Ba or Ca; M<2> is Co or Fe; M<3> is Pt or Pd; 0.005<=X<=0.2) can be obtained by the following method: an aqueous solution of (A) nitrates or acetates of the constituent metallic elements of the above multiple oxide and (B) citric acid is evaporated to dryness to form a citric acid complex which is then heated in a vacuum or an inert gas atmosphere at >=350 deg.C into a preliminarily baked form, which is then baked in an oxidative atmosphere, thus affording the objective multiple oxide where >=90wt.% of the M<3> metal (Pt or Pd) exist in the crystal lattice.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a perovskite structure composite oxide which can be used as an exhaust gas purifying catalyst, a combustion catalyst for natural gas or the like, or an adsorbent for harmful substances such as nitrogen oxides, and the like. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art A catalyst for removing harmful substances such as nitrogen oxides, hydrocarbons and carbon monoxide contained in exhaust gas discharged from an internal combustion engine or a factory by oxidation / reduction, natural gas, synthetic gas, etc. Noble metal elements such as platinum and palladium are said to be effective as combustion catalysts or adsorbents for organic substances such as nitrogen oxides.

Recently, attention has been paid to a crystal in which the above noble metal element is contained in a crystal having a perovskite structure. The perovskite type structure is one form of crystal form found in the composite oxide.

When the noble metal element is included in the crystal lattice of this structure, the noble metal particles are made finer to improve the dispersibility, and further, lattice defects contributing to the catalytic activity and the adsorption activity are appropriately generated, so that the noble metal element Properties such as catalytic activity and adsorption activity are improved.

Conventionally, a perovskite-type composite oxide having such characteristics has a chemical formula of M ¹ M ² _1-X M
^{A structure having a structure represented by 3} _X O ₃ (wherein, M ¹ is a rare earth element such as lanthanum and cerium, M ² is cobalt, iron, aluminum, and M ³ is a noble metal element) has been proposed (Japanese Patent Application Laid-Open No. 2000-242242). Japanese Laid-Open Patent Publication No. 50-83295, JP-A No. 2-1690.
33, JP-A-3-131342, JP-A-3
-200058).

For example, the catalyst composed of this perovskite type composite oxide can remove a certain amount of harmful substances in the exhaust gas. However, as the problem of environmental pollution has become more serious in recent years, the purification standards for exhaust gas have become more stringent, and the purification activity of this type of conventional catalyst is insufficient.

[0007]

Therefore, in order to elucidate the cause, the present inventors have examined the conventional perovskite type structure composite oxides, particularly the existence form of the noble metal element in the crystal lattice.

According to this, it was found that in the conventional one, the amount of the noble metal element contained in the crystal lattice of the perovskite type structure was as small as 85% or less. If the proportion of the noble metal element present in the crystal lattice is low, the particles of the noble metal element that do not enter the crystal lattice will not be finely divided and will be aggregates of about 40Å size. Therefore, the degree of dispersion of the noble metal element in the composite oxide does not increase, and the properties such as catalytic activity are not improved.

The inventors of the present invention have made further studies and considered that the existence form of the noble metal element in the crystal lattice is related to the preparation of the composite oxide, and paid attention to the method for producing the composite oxide.

In the conventional production of complex oxides, (a) a metal element of a metal element constituting the chemical formula of the perovskite structure, or an oxide, a hydroxide, or a metal salt is used as a starting material and these powders are mixed. And then firing, or (b) a method in which the catalyst carrier is impregnated with a mixed aqueous solution of the nitrate of the above metal element and then heat treated, and (c) addition of citric acid to the salt of the above metal element (nitrate or acetate). It is performed by a method of forming a citric acid complex using the mixed solution, and then baking the complex.

In the case of powder mixing of (a), since the mixing is insufficient, it becomes difficult to uniformly disperse the constituent elements. Therefore, the ratio of the noble metal element present in the crystal lattice does not increase, and the ratio becomes about 85% at the maximum.

Further, in the case of using the mixed aqueous solution of nitrate of metal element (b), the metal ions become unstable in the aqueous solution, resulting in uneven concentration and sedimentation of heavy elements and light elements. Therefore, the noble metal element becomes non-uniform in the drying step after impregnation into the catalyst carrier, and the crystallization rate during firing is reduced. Further, the proportion of the noble metal element present in the crystal lattice is also reduced.

In the case of forming the citric acid complex of the metal element (c), the citric acid complex is heated to 200 to 30 in a vacuum in order to decompose the citric acid complex by heating before forming and firing.
Heating at 0 ° C. However, since this heating is insufficient, the salt of the metal element (nitrate or acetate), which is the starting material, remains. Therefore, the diffusion of metal ions before crystallization is not smoothly performed, and the ratio of the noble metal element present in the crystal lattice is reduced.

As described above, the conventional complex oxide having the perovskite structure has a problem in the existence form of the noble metal element in the crystal lattice, and the properties such as catalytic activity and adsorption activity are not improved when it is used as a catalyst. .

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a perovskite structure composite oxide excellent in characteristics such as catalytic activity and adsorption activity, and a method for producing the same. .

[0016]

[Means for Solving the Problems]

(Structure of First Invention) The perovskite structure composite oxide (referred to as the first invention) of the present invention is M ¹ M ² _1-X M ³ _X O ₃
(In the formula, M ¹ is lanthanum, strontium, cerium,
At least one of barium and calcium, M ² is at least one of cobalt and iron, M ³ is at least one of platinum and palladium, and X is 0.00
5 ≦ X ≦ 0.2), the M ³ element in the above formula is characterized in that 90% or more thereof is present in the crystal lattice. .

(Structure of the Second Invention) The method of manufacturing the perovskite structure composite oxide of the present invention (referred to as the second invention) is as follows.
M ¹ M ² _1-X M ³ _X O ₃ (wherein M ¹ is at least one of lanthanum, strontium, cerium, barium, and calcium, M ² is at least one of cobalt and iron, and M ³ is At least one of platinum and palladium, and X is 0.005 ≦ X ≦ 0.2), and an aqueous solution in which a salt of a metal element constituting the perovskite-type structural composite oxide and citric acid are dissolved is prepared. A first step of preparing, a second step of forming a complex of the metal element and citric acid by drying the aqueous solution, and a tentative process by heating the complex in vacuum or in an inert gas at 350 ° C. or higher. It is characterized by comprising a third step of baking and a fourth step of forming the perovskite type structure composite oxide by baking the pre-baked body in an oxidizing atmosphere.

[0018]

[Action]

(First effect of the invention) The present first _{^{invention, M 1 M 2 1-X}} M 3
_{In X} O ₃ , 90% or more of the M ³ element (platinum or palladium) is present in the crystal lattice, so most of the platinum or palladium particles become finer (about 2Å) and become active species such as catalysts. The degree of dispersion is improved. In addition, platinum or palladium, which does not exist in the crystal lattice, has a particle size of about 40Å
Since it becomes aggregates of size, it does not become an active species such as a catalyst. However, in the first invention, since the amount of platinum or palladium is small, this effect is extremely small. Furthermore, the element of M ³ is not present in the crystal lattice, even not present in the crystal lattice elements M ¹ paired with the M ^3. The element of M ¹ which does not exist in this crystal lattice becomes an oxide and is mixed as an impurity. This impurity does not function as an active species of the catalyst or the like, and is deposited on the active site of the catalyst or the like to reduce the activity. However, such impurities are small in the first invention.

(Operation of the Second Invention) In the second invention, a citric acid complex of a metal element forming a perovskite structure complex oxide is formed. In this citric acid complex, the metal ion is linked to the carboxyl group of citric acid, so that the metal ions form a state in which the metal ions are uniformly close to each other with citric acid at the center. At the same time, it prevents metal ion concentration unevenness and sedimentation. Therefore, the metal element easily enters the crystal lattice at the time of firing to form the perovskite type composite oxide.

Before heating, the citric acid complex is heated in vacuum or in an inert gas at 350 ° C. or higher to prevent citric acid from entering the crystal lattice and a salt of the starting metal element. Most of the residue (organic matter, or nitrate radical when nitrate is used, for example) is removed by thermal decomposition, so that the metal element can smoothly enter the crystal lattice. Therefore, the existence ratio of the metal element in the crystal lattice increases.

[0021]

【The invention's effect】

(Effect of the first invention) In the perovskite structure composite oxide of the first invention, since 90% or more of platinum or palladium is present in the crystal lattice as metal ions, the particles of platinum or palladium are finely divided and the dispersity is high. As the crystal lattice defects are appropriately generated, the properties such as catalytic activity and adsorptivity are improved.

(Effect of the Second Invention) In the second invention, the perovskite type structure composite oxide excellent in the characteristics of the first invention can be produced.

[0023]

EXAMPLES Specific examples of the present invention will be described below.

(Specific Example of First Invention) The perovskite structure composite oxide of the first invention is M ¹ M ² _1-X M ³ _X O ₃
(In the formula, M ¹ is lanthanum, strontium, cerium,
At least one of barium and calcium, M ² is at least one of cobalt and iron, M ³ is at least one of platinum and palladium, and X is 0.00
5 ≦ X ≦ 0.2), and 90% or more of platinum or palladium of M ³ is present in the crystal lattice.

In the first aspect of the present invention, 90% or more of platinum or palladium is present in the crystal lattice. If the existing amount is less than 90%, crystal lattice defects are not generated, and properties such as catalytic activity and adsorptivity are not improved.

The X-ray diffraction analysis method is used to measure the amount of platinum or palladium present in the crystal lattice. Make a mixed powder by mixing platinum or palladium metal particles into a perovskite structure composite oxide that does not contain platinum or palladium, select an appropriate analysis line and measure its intensity ratio to determine the relationship between the intensity ratio and the mixture ratio. The mixture ratio of the components is obtained by collating with the calibration curve shown.

In the above formula, X is 0.005≤X≤.
Set to 0.2. The perovskite structure complex oxide represented by M ¹ M ² _1-X M ³ _X O ₃ has a simple cubic lattice structure as an ideal lattice. M ² and M ³ are surrounded by 6 O atoms and have 6 coordination. M ¹ is surrounded by 12 O atoms and has 12 coordinations. Therefore, in an ideal lattice, M ^2, M ³ is necessary that the ionic radius of the having a valence that can keep in hexa-coordinated and M ² at the same time M ³ are as close as possible.
The crystal lattice becomes distorted according to the degree to which the ionic radii of M ² and M ³ differ. M with different ionic radius with respect to M ^2
As the amount of ³ increases, the strain of the crystal form increases.
Although it is not uniquely determined by the relationship between the ionic radii of M ² and M ³ , when X is larger than 0.2, the strain becomes large and M ³ does not enter the crystal lattice. Therefore, the existing amount in the crystal lattice does not exceed 90%. On the other hand, M ³
Is well within the crystal lattice when X is less than 0.005,
Since the amount is small, the effect as a practical active species such as a catalyst cannot be exhibited.

Since the perovskite structure composite oxide of the first aspect of the present invention has improved characteristics such as catalytic activity and adsorptivity, an exhaust gas purifying catalyst (purifying hydrocarbons, purifying nitrogen oxides, etc.), It can be used as a nitrogen oxide adsorbent (nitrogen oxide adsorption removal), a combustion catalyst (combustion of vaporized fuel such as natural gas or petroleum gas), and the like.

When used as a catalyst, it is preferable that the perovskite structure composite oxide of the first invention is dispersed and supported on a refractory inorganic carrier such as cordierite to form a catalyst. When carrying this dispersion, it is preferable to use PVA (polyvinyl alcohol), carbon black, or the like as a dispersion medium in order to carry the composite oxide as highly dispersed as possible. Further, as the dispersant or binder, alumina sol, silica sol, zirconia sol or the like can be used. The amount used varies depending on the purpose and the state of use, but a solid content ratio of about 3 to 15% by weight is preferable, and the necessary minimum amount is selected in order not to reduce the catalyst activity.

(Specific Example of Second Invention) In the method for producing a perovskite type composite oxide of the second invention, M ¹ M ^{2 is used.}
_1-X M ³ _X O ₃ (wherein M ¹ is at least one of lanthanum, strontium, cerium, barium and calcium, M ² is at least one of cobalt and iron,
M ³ is at least one of platinum and palladium, and X is 0.005 ≦ X ≦ 0.2), and a salt of a metal element constituting the perovskite structure composite oxide and citric acid are dissolved. An aqueous solution is prepared (first step), the aqueous solution is dried to form a citric acid complex of the metal element (second step), and the citric acid complex is heated at 350 ° C. or higher in a vacuum or an inert gas. Preliminary firing (third step) and then firing in an oxidizing atmosphere (fourth step).

In the first step, an aqueous solution in which a salt of a metal element and citric acid are dissolved is prepared.

The salt of the metal element is preferably in the form of nitrate or acetate. This is because the remaining substances other than the metal element can be decomposed by the calcination in the third step. For example, in the case of a hydrochloride, chlorine remains and affects characteristics such as catalytic activity and adsorption activity.

For example, as the nitrate of the element M ^{1 in} the above formula, La (NO ₃ ) ₃ .6H ₂ O, Sr (NO
_{3) 2, Ce (NO 3} ) 3 · 6H 2 O, Ba (NO 3)
_{2, Ca (NO 3) 3} · 4H 2 O , and the like, also,
As the acetate salt of the element of M ¹ , La (CH ₃ COO) ₃
・ 3 / 2H ₂ O, Sr (CH ₃ COO) ₂・ 1 / 2H ₂
O, Ce (CH ₃ COO) ₃ · H ₂ O, Ba (CH ₃ C
OO) ₂ , Ca (CH ₃ COO) ₂ · H ₂ O and the like. The nitrate of the element of M ² is Co (NO ₃ ) _{2
· 6H 2 O, Fe (NO} 3) 3 · 9H 2 O and the like, and as the acetic acid salt of the element of M ² is, Co (CH ₃
COO) ₂ · 4H ₂ O, and the like. Examples of the nitrate of the element of M ³ include dinitrodiammine platinum nitrate, dinitrodiammine palladium nitrate and the like. Also,
Pt (NH ₃ ) ₄ (OH) ₂ can also be used as a substitute for the dinitrodiammine platinum nitrate.

The salts of these metal elements are represented by the above formula M ¹ M ² _1-X
The compounding ratio is such that M ³ _X O ₃ is formed.

The content of citric acid is such that M ^{1 to be} formed is
_{^{M 2 1-X M 3 X}} O 3 preferably set to 2 to 2.4 mols relative to 1 mol. If the amount is less than 2 mol, complex formation may be difficult, and if it exceeds 2.4 mol, complex formation may be sufficient, but uniform mixing of metal elements may be difficult.

As a method for preparing an aqueous solution in which a salt of a metal element and citric acid are dissolved, for example, a salt of a metal element is dissolved in ion-exchanged water, and citric acid is dissolved in another ion-exchanged water. There is a method of mixing both.

In the second step, the citric acid complex of the metal element is formed by drying the aqueous solution.

[0038] As the drying condition, a condition for quickly removing water in a temperature range where the citric acid complex is not decomposed is suitable. For example, the temperature may be room temperature to 150 ° C., and the time may be 2 to 12 hours.

In the third step, the citric acid complex of the metal element is heated at 350 ° C. or higher in vacuum or in an inert gas to be calcined.

When the calcination atmosphere is an oxidizing atmosphere, decomposition of citric acid from the citric acid complex and residues (organic substances, nitrates, etc.) from salts of metal elements is not promoted. Therefore, it is in vacuum or in an inert gas. It should be noted that a vacuum is more preferable than an inert gas because the decomposition is promoted.

If the heating temperature is lower than 350 ° C., the residual substances (organic substances, nitrate radicals, etc.) from the citric acid and the salt of the metal element as the starting material cannot be decomposed by heating and remain. The upper limit of the heating temperature is preferably 500 ° C. 500
There is no problem even if the temperature exceeds ℃, but 500 ℃ for calcination
Is sufficient, and waste of energy and damage to the pre-baking device are not preferable.

When heating, it is preferable to slowly raise the temperature from 80.degree. This is because the residue from the citric acid and the salt of the metal element starts to decompose from around 130 ° C., and the decomposition is accelerated by taking a temperature in this range for a long time. At 350 ° C. or higher, it is preferable to keep the temperature for about 2 to 3 hours.

A calcined body is formed by this step.

In the fourth step, the calcination body is fired.

The firing method may be any method, but an oxidizing atmosphere in which oxygen is present, such as in the air, is used to form an oxide.

The firing temperature is 700 to 950.
The range of ° C is preferred. At a temperature lower than 700 ° C., crystals having a perovskite structure are difficult to grow. Also, 950
If the temperature exceeds ℃, the crystal growth will proceed too much, so the precious metal that has a proper lattice defect and exists in the lattice may come out of the crystal lattice, or the specific surface area may decrease and the activity may decrease. There is.

A calcination product can be obtained even if the calcination time is about 1 hour, but the longer the time, the higher the crystallization rate of the composite oxide. Therefore, 2 to 5 hours are preferable.

Examples of the present invention will be described below.

Example 1 21.67 g (0.05 mol) of lanthanum nitrate was dissolved in 50 ml of deionized water. Also, cobalt acetate 11.5
6 g (0.045 mol) was dissolved in 50 ml of deionized water. Also, dinitrodiamino platinum nitric acid 21.35 g
(0.005 mol) was dissolved in 30 ml. In addition, 25.22 g (0.12 mol) of citric acid was added to ion-exchanged water 12
It was dissolved in 0 ml. These four kinds of aqueous solutions were mixed to prepare a mixed aqueous solution of about 250 ml (first step).

This mixed aqueous solution was evaporated to dryness in a hot water bath at 80 ° C. for about 4 hours while reducing the pressure with an evaporator to prepare a citric acid complex (second step).

The citric acid complex was depressurized (1
0 ^-2 torr or less) 80 by a mantle heater while
The temperature was slowly raised from 0 ° C to 400 ° C so that the temperature did not rise sharply. Note that acetic acid and citric acid began to decompose at around 130 ° C. At 250 to 400 ° C., nitrate radicals were decomposed and a yellow gas was generated. Therefore, it was confirmed that the generated gas disappeared, and this heat treatment was completed (about 3 hours). In this way, a calcinated body from which organic substances and nitrates were removed was prepared (third step).

This calcinated body was made into a powder, placed in a crucible and fired in an air atmosphere at a temperature range of 700 to 950 ° C. for 3 hours (fourth step).

As a result, a perovskite structure composite oxide having a composition represented by LaCo _0.9 Pt _0.1 O ₃ was produced.

Examples 2 to 5 In the same manner as in Example 1, LaCo _0.8 Pt _0.2 O ₃ (Example 2), La _0.9 Ce _0.1 Co _0.98 Pt _0.02 O ₃ (Example 3), La _0.8 Sr _0.2 Fe _0.95 A perovskite structure composite oxide having a composition represented by Pd _0.05 O ₃ (Example 4) and Sr _0.9 Ba _0.1 Co _0.85 Pd _0.15 O ₃ (Example 5) was produced.

[0055] Comparative Example 1 LaCo _0.9 Pt _0.1 O ₃ so as to have the composition represented by, lanthanum oxide (La ₂ O _3, molecular weight 326) 65.
20 g, cobalt carbonate (CoCO ₃ , molecular weight 119) 2
1.42 g, and platinum oxide (PtO ₂ · xH ₂ O, P
4.68 g (t83.25%) was crushed and mixed in a mortar. This mixed powder is put in a platinum crucible and heated in air at 950-100.
Baking at 0 ° C. for about 3 days.

Comparative Example 2 A homogeneous mixed aqueous solution of lanthanum nitrate, cobalt acetate, dinitrodiamine platinum and citric acid was prepared in the same manner as in the first step of Example 1 so that the composition was represented by LaCo _0.9 Pt _0.1 O _3. 250 ml was made. Next, water was evaporated to dryness in the same manner as in Example 1 to prepare a citric acid complex. This citric acid complex was heated in vacuum to 300 ° C. to prepare a pre-baked body. At this time, only a slight amount of yellow gas was observed, and nitrate radicals were hardly decomposed and remained in the solid matter. After cooling, the pre-baked body was taken out of the vacuum furnace, placed in a crucible, and baked in an air atmosphere at 750 ° C. for 3 hours.

Comparative Example 3 The following mixed aqueous solution was prepared so as to have a composition represented by LaCo _0.9 Pt _0.1 O ₃ . First, lanthanum nitrate 2
1.67 g (0.05 mol) was dissolved in 50 ml of deionized water. Also, 11.56 g of cobalt acetate (0.04
5 mol) was dissolved in 50 ml of deionized water. The lanthanum nitrate aqueous solution and the cobalt acetate aqueous solution are mixed to obtain 10
It was made 0 ml and stirred with a magnetic stirrer. In addition, dinitrodiammine platinum nitric acid 21.35 g (0.0
An aqueous solution prepared by dissolving (05 mol) in 30 ml of ion-exchanged water was added to and mixed with the above mixed aqueous solution, followed by stirring.

Next, the resulting mixed aqueous solution was mixed while being heated by a magnetic stirrer with a heater to evaporate water. A precipitate was formed during the evaporation to give a heterogeneous mixed solution, which was continued to be heated and evaporated to dryness.

Then, the dried solid was pre-baked at 400 ° C. for 3 hours in the atmosphere. At this time, it was confirmed that yellow gas was generated and nitrate radicals were decomposed and disappeared.

The calcined body was further heated in the atmosphere at 750 ° C.
Baked for 3 hours.

The abundances of platinum and palladium in the crystal lattice of the fired bodies of Examples 1 to 4 and Comparative Examples 1 to 3 were measured by X-ray diffraction analysis. The results are shown in Table 1. Among them, Examples 1, 2 and Comparative Examples 1, 2 and LaCoO ₃ (X in the composition formula of the perovskite type structure)
X-ray diffraction chart (of which = 0) is shown in FIG.
Examples 1 and 2 and LaCo _0.7 Pt _0.3 O ₃ (where X = 0.3 in the compositional formula of the perovskite structure), L
The X-ray diffraction chart of aCoO ₃ is shown in FIG.

[0062]

[Table 1]

As is clear from Table 1 and FIGS.
In this example, it can be seen that 90% or more of platinum and palladium are present in the crystal lattice.

Further, the catalyst performance of each fired body was evaluated as follows.

Powder obtained by crushing the fired body was pressed by a tablet molding machine to form a plate having a thickness of about 1 mm, and then crushed to 1 to 2 mm.
Pellets. About this pellet (a) NO
Evaluation tests of _X purification performance, (b) NO _X adsorption performance, and (c) hexane conversion performance were conducted.

(A) NO _x purification performance: A swirl chamber type diesel engine (2.45 l) was operated under domestic 10-mode test conditions to generate actual exhaust gas. 2 g of the above-mentioned pellet of 1 to 2 mm was packed in a flow type fixed bed kept at 300 ° C.,
The actual exhaust gas was contacted at a space velocity of 192000 / hour, and the NO _x concentration was measured at the outlet with an automobile exhaust gas analyzer (manufactured by Horiba, Ltd.). The NO _X purification rate was calculated from the NO _X concentration before and after the pellet filling.

(B) NO _X adsorption performance: An atmospheric pressure fixed bed flow type reactor was filled with 4 cc of the above pellets of 1 to 2 mm,
Hold at 200 ° C. The model gas (NO ₂
200 ppm, O ₂ 10%, N ₂ balance) 1 l / m
in (space velocity 15,000 / hour), NO _{2 at} outlet
The concentration was measured with an exhaust gas analyzer (manufactured by Best Instruments Co., Ltd.).

(C) Hexane conversion performance: The pellets (7 cc) were packed in an atmospheric fixed bed flow reactor. Model gas (hexane (C ₆ H ₁₄ ) 500 ppm,
Oxygen (O ₂ ) 5%, nitrogen (N ₂ ) balance) 3.3 l
/ Min (space velocity 28600 / hour), and the pellets were contacted. During the process of raising the reaction temperature from 150 ° C to 350 ° C, the output gas is sampled appropriately and the hexane is quantitatively analyzed with a gas chromatograph having an FID detector. The hexane purification rate is calculated from the ratio of the input gas and the output gas. Was measured. The pellet temperature when the hexane purification rate reached 50% was determined.

The above (a) NO _x purification performance, (b) NO _x
Table 2 shows the evaluation test results of the adsorption performance and (c) hexane conversion performance.

[0070]

[Table 2]

As is clear from Table 2, all performances of this example are superior to those of the comparative example.

[Brief description of drawings]

FIG. 1 is a diagram showing the X-ray diffraction results of perovskite type composite oxides in the present example and comparative example.

FIG. 2 is a diagram showing an X-ray diffraction result of a perovskite structure composite oxide in this example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Sugiura 1 41, Yokoshiro, Nagakute-cho, Aichi-gun, Aichi-gun, Nagatoko-Chi, Toyota Central Research Institute Co., Ltd. (72) Hideaki Ueno 1 Toyota-cho, Toyota-shi, Aichi Address Toyota Motor Co., Ltd. (72) Inventor Tatsushi Mizuno 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd.

Claims (2)

[Claims] 1. M ¹ M ² _1-X M ³ _X O ₃ (wherein M ¹ is at least one of lanthanum, strontium, cerium, barium and calcium, and M ² is at least cobalt and iron. On the other hand, M ³ is at least one of platinum and palladium, and X is 0.005 ≦ X ≦ 0.2.
In the perovskite structure composite oxide represented by the formula (1), 90% or more of the element of M ³ in the above formula is present in the crystal lattice, the perovskite structure composite oxide. 2. M ¹ M ² _1-X M ³ _X O ₃ (wherein M ¹ is at least one of lanthanum, strontium, cerium, barium and calcium, and M ² is at least cobalt and iron. On the other hand, M ³ is at least one of platinum and palladium, and X is 0.005 ≦ X ≦ 0.2.
The first step of preparing an aqueous solution in which a salt of a metal element constituting the perovskite-type structure composite oxide represented by (4) and citric acid are dissolved; and a step of combining the metal element and citric acid by drying the aqueous solution. A second step of forming a complex, a third step of calcining the complex by heating the complex in vacuum or an inert gas at 350 ° C. or higher, and a perovskite structure by calcining the calcined body in an oxidizing atmosphere. A method for producing a perovskite-type structure composite oxide, which comprises a fourth step of forming a composite oxide.